The EIP 29/29 gene of Drosophila melanogaster is regulated by the steroid hormone ecdysone. The gene is of particular interest because in two Drosophila cell lines EIP 28/29 transcripts increase in abundance as a very early and probably primary effect of ecdysone. The structure of this inducible, Kc major transcription unit has been solved. There is evidence that this transcription unit is hormonally induced in many Drosophila tissues. There is also evidence for alternative, overlapping transcription units which are tissue-specific and some of which may be ecdysone-regulated. We propose two lines of work. First, we propose to study the Kc major promotor already identified with the goal of identifying those sequence elements required for its promotor activity and regulation. Second, we propose to analyze the expression of the EIP 28/29 gene in development with special emphasis on the problems of defining the structures of the various EIP 28/29 transcripts, describing their regulation, and characterizing their protein products. The results of the proposed study will contribute to our understanding at the molecular level of steroid hormone action and will enrich our understanding of the roles of such hormones in development.